Radiation detectors that detect a radiation dose by collecting electrons and ions of gas ionized by radiation include two electrodes (cathode and anode) in a vessel filled with gas, and detect the radiation dose by applying a voltage between the two electrodes and collecting, at the electrodes, electrons and ions of gas ionized by radiation.
As such radiation detectors, an ionization chamber mode refers to one having a voltage-electrode configuration in which a voltage to be applied between a cathode and an anode is set within a range not amplifying a gas ionization signal generated by radiation, and a proportional counter mode refers to one having a voltage-electrode configuration in which an electron avalanche is caused by applying a high electric field in the vicinity of an anode so as to amplify a signal.
Conventional radiation detectors include one configured by arranging a thin linear anode at the center of a cylindrical sealed vessel that serves as a cathode, and filling the vessel with ionization gas such as an argon (Ar) gas mixed with an organic gas. In the vessel of the radiation detector, ionization gas is ionized by radiation, and generated electrons and ions move by an electric field applied between the cathode and the anode. At this time, an electron avalanche especially occurs in the vicinity of the anode, and the radiation is counted as a large pulse signal.
Further, there is a radiation detector that detects a radiation dose using different types of ionization gas depending on the energy of radiation to be measured, such as X-rays and γ-rays. For example, when detecting X-rays having low energy, gas of an element whose absorption coefficient is large and atomic number is large is used. Meanwhile, when detecting neutron rays, since neutron rays do not ionize gas, gas such as helium (He3) or boron trifluoride (BF3) that generates charged particles by nuclear reaction with neutron rays is used as the ionization gas. Further, there is a radiation detector that detects neutron rays by application of boron 10 (B10), uranium 235 (U235) or the like to the inside of a vessel that is used as a cathode, and converting the rays into charged particles in the vessel, thereby causing similar ionization effects (see Patent Documents 1, 2 and 3).